A shaft assembly (200) for selectively interconnecting an end effector (400) and an electromechanical power source, the shaft assembly comprising: an outer tube (210)； a rotating drive shaft supported therein； a proximal neck housing (232) supported at a distal end (210b) of the outer tube； a distal neck housing (236) rotatably connected to the proximal neck housing (232), in which a distal end of the distal neck housing is configured and adapted for the operative connection with the end effector (400) ； a pivot (234) that interconnects the proximal neck housing (232) and the distal neck housing (236)； and a gear train (238) supported in the proximal neck housing, in the pivot and in the distal neck housing, in which the gear train includes: a proximal gear (238a) rotatably supported in the housing of proximal neck (232) and coupled to a distal end of the rotary drive shaft； an intermediate gear (238b) rotatably supported on the pivot (234) and in operative engagement with the proximal gear； a distal gear (238c) rotatably supported in the distal neck housing (236) and in operative engagement with the intermediate gear； and characterized by a pair of output gears (239a, 239b) rotatably supported in the distal neck housing (236) and each in operative engagement with the distal gear, in which each output gear defines a coupling socket (239a1, 239b1) each configured to selectively receive the drive shaft of the end effector.Un conjunto de eje (200) para interconectar selectivamente un efector de extremo (400) y una fuente de energía electromecánica, comprendiendo el conjunto de eje: un tubo exterior (210)； un eje de accionamiento giratorio soportado en el mismo； una carcasa de cuello proximal (232) soportada en un extremo distal (210b) del tubo exterior； una carcasa de cuello distal (236) conectada de manera giratoria a la carcasa de cuello proximal (232), en la que un extremo distal de la carcasa de cuello distal está configurado y adaptado para la conexión operativa c
